The presumption of innocence, sometimes referred to by the Latin expression Ei incumbit probatio qui dicit, non qui negat (the burden of proof is on he who declares, not on he who denies), is the principle that one is considered innocent until proven guilty. Application of this principle is a legal right of the accused in a criminal trial, recognised in many nations. The burden of proof is thus on the prosecution, which has to collect and present enough compelling evidence to convince the trier of fact, who is restrained and ordered by law to consider only actual evidence and testimony that is legally admissible, and in most cases lawfully obtained, that the accused is guilty beyond a reasonable doubt. If reasonable doubt remains, the accused is to be acquitted.
The sixth century Digest of Justinian (22.3.2) provides, as a general rule of evidence: Ei incumbit probatio qui dicit, non qui negat—"Proof lies on him who asserts, not on him who denies". It is there attributed to the second and third century jurist Paul. When this rule is applied to criminal process (whether or not that was done in Roman law itself), it places the burden of proof upon the accuser, which has the corollary that the accused is presumed to be innocent.
In sources from common law jurisdictions, the expression appears in an extended version, in its original form and then in a shortened form (and in each case the translation provided varies). As extended, it is: Ei incumbit probatio, qui dicit, non qui negat; cum per rerum naturam factum negantis probatio nulla sit—"The proof lies upon him who affirms, not upon him who denies; since, by the nature of things, he who denies a fact cannot produce any proof." As found in its original form, it is (as above): Ei incumbit probatio qui dicit, non qui negat—"The proof lies upon the one who affirms, not the one who denies." Then, shortened from the original, it is: Ei incumbit probatio qui—"the onus of proving a fact rests upon the man who".